. . .were/are written in house, using the "almost-final" beta versions of the games. Of course, this in itself led to corrections, as the Prima staff were more thorough in playtesting than the volunteers usually used. I don't know where I got this info/theory--probably from some long-ago publication like "Computer Gaming World" or "Computer Games, Strategy Plus."
As for beta-testing in itself: Papa Elf and I beta-tested the old AOL (America OnLine, for you youngsters.) It was a painful affair, using a ve-e-e-r-y slo-o-o-w dial-up modem. Of course, anyone attempting to make a call from one of the phone extensions (we had three) would knock you offline immediately. The kids were adolescents then, just at the stage where they just HAD to talk to their friends at all hours. (Cell? What is this cell of which you speak?) We loved AOL back then, despite the inconvenience.